Rheological Properties of Particle-Stabilized Emulsions

We have studied the rheological properties of fumed silica particle-stabilized emulsions. Two particles of different polarity were considered, the first more hydrophilic “Aerosil R7200,” the second more hydrophobic “Aerosil R972.” These particles flocculate and probably form a network at the investigated concentration. The flow curves of emulsions stabilized by a single type of particles exhibit yield stress, shear-thinning behavior and thixotropy. Moreover they display rheological features typical of gels. These features are attributed to strengthening of the particle network by droplets. Moreover the rheological properties of w/o emulsions stabilized by hydrophobic are similar to the ones of o/w emulsions stabilized by hydrophilic particles. The rheological properties of o/w emulsions stabilized by mixtures of hydrophilic and hydrophobic particles have then been studied by keeping the total particle concentration constant and varying the mass ratio between particles. The results show that when the hydrophobic particle concentration increases, the viscosity and stability of emulsions decrease establishing evidence that the network is weakened due to preferential orientation of hydrophobic particles towards the oil phase.     

Investigations into the electrical and coalescence behaviour of water-in-crude oil emulsions in high voltage gradients

The stability of water-in-crude oil emulsions when subjected to high voltage electric fields depends on the nature of the crude oil and the presence of chemical additives. Optical microscopy, conductivity and coalescence measurements have revealed two distinct types of behaviour, designated type I and type II. These are shown to be related to the crude oil/water interfacial rheological properties. For incompressible crude oil/water films, droplet—droplet coalescence is hindered and chains of water droplets are established. These increase the electrical conductivity of the emulsion (type I behaviour). On the other hand, efficient droplet—droplet coalescence accompanied by minimal conduction occurs in electric fields if the interfacial film is compressible (type II).     

Laminar Flow Emulsification Process to Control the Viscosity Reduction of Heavy Crude Oils

The formation of heavy crude oil in water (O/W) emulsion by a low energy laminar controlled flow has been investigated. The emulsion was prepared in an eccentric cylinder mixer. Its geometry allows the existence of chaotic flows that are able to mix well highly viscous fluids. This new mixer design is used to produce high internal phase ratio emulsions for three oils: castor oil and two heavy crude oils of different initial viscosity (Zuata and Athabasca crude oils). The influence of the stirring conditions, geometrical parameters, and water volume fraction on the rheological properties of the resulting O/W emulsion is studied.     

Boosting the stability of protein emulsions by the synergistic use of proteins and clays

The preparation and the properties of high-pressure emulsions based on five different proteins are reported. As proteins, we used the well-studied bovine serum albumin (BSA), a biotechnical produced hydrophobin called H Star Protein B? (HPB), a protein isolate from soybeans, a wheat protein isolate (Plantasol W), and a commercially available yeast extract. All emulsions were characterized by visual appearance, light microscopy, conductivity, and rheological measurements. Beside the emulsion based on soy protein isolate, all other samples showed phase separation under the used conditions (0.5 wt.% protein; 50 wt.% oil). Plantasol W and yeast extract formed the most unstable emulsions showing typical instability processes like coalescence. Gel-like properties have been observed for emulsions based on BSA, soy protein isolate, and HPB. The same proteins were also used to stabilize emulsions after their adsorption on clay particles. Interestingly, all emulsions had gel-like properties with a yield stress value and were stable to the used conditions. It is concluded that the gel character results from the stickiness of the protein covered oil droplets and is independent from the used protein type. The proteins which are adsorbed on the oil droplets can still interact and bind to proteins on other oil droplets.     

Interface composition of multiple emulsions: rheology as a probe

We have investigated the dynamic rheological properties of concentrated multiple emulsions to characterize their amphiphile composition at interfaces. Multiple emulsions (W1/O/W2) consist of water droplets (W1) dispersed into oil globules (O), which are redispersed in an external aqueous phase (W2). A small-molecule surfactant and an amphiphilic polymer were used to stabilize the inverse emulsion (W1 in oil globules) and the inverse emulsion (oil globules in W2), respectively. Rheological and interfacial tension measurements show that the polymeric surfactant adsorbed at the globule interface does not migrate to the droplet interfaces through the oil phase. This explains, at least partly, the stability improvement of multiple emulsions as polymeric surfactants are used instead of small-molecule surfactants.     

Bitumen-in-Water Emulsions: An Overview on Formation,Stability, and Rheological Properties

This paper describes the most relevant issues associated with the development of a technology; the formation of highly concentrated bitumen-in-water emulsions. Viscosity values for bitumen-in-water emulsions, containing between 70 and 85% (v/v) of bitumen, have been found to be several order of magnitude lower than the viscosity of the hydrocarbon itself. Thus, these emulsions, have potential applications in the processes of production, transportation, handling and commercialization of these extremely highly viscous hydrocarbons. The emulsions, the properties of which are discussed in this paper, were stabilized with mixtures of nonionic and natural surfactants (1,2) and formed using the HIPR (high internal phase ratio) technique (3). Information on the conditions required to produce emulsions with very narrow droplet diameter distributions is given. Results indicate that the mean droplet diameter, the droplet diameter distribution, and the bitumen volume fraction, significantly modify the rheological behavior. Emulsion stability was measured by following changes in the mean droplet diameter and in the rheological parameters with storage time.     

Properties of emulsions and free emulsion (Aqueous) films stabilized with hexylamine-modified silica

The type and stability of emulsions, as well as the stability and thickness of free aqueous emulsion films stabilized with Aerosil-hexylamine mixtures, have been studied. The rheological characteristics (dynamic yield stress, elasticity modulae, and viscosity) have been measured for suspensions from which emulsions and films have been prepared. It has been shown that the properties of the films depend on the rheological properties of the suspensions.     

Stability of Water/Crude Oil Systems Correlated to the Physicochemical Properties of the Oil Phase

A characterization of 30 crude oils has been performed to determine the relative level of influence that individual parameters have over the overall stability of w/o emulsions. The crude oils have been analyzed with respect to bulk and interfacial properties and the characteristics of their w/o emulsions. The parameters include compositional properties, acidity, spectroscopic signatures in the infrared and near‐infrared region, density, viscosity, molecular weight, interfacial tension, dilational relaxation, droplet size distribution, and stability to gravitationally and electrically induced separation. As expected, a strong covariance between several physicochemical properties was found. Near‐infrared spectroscopy proved to be an effective tool for crude oil analysis. In particular, we have showed the importance of the hydrodynamic resistance to electrically‐induced separation (static) in heavy crude oil‐water emulsions. A rough estimate of the drag forces and dielectrophoretic forces seemed to capture the difference between the 30 crude oils. Given enough time, water‐in‐heavy oil emulsions could be destabilized even at very low electric field magnitude (d.c.). When droplets approach each other in an inhomogeneous electric field, strong dielectrophoretic forces disintegrate the films and result in coalescence. The relative contribution from film stability to the overall emulsion stability may therefore be very different in a gravitational field compared to that in an electrical field.     

The heat stability of milk protein-stabilized oil-in-water emulsions: A review

The knowledge on the factors affecting the heat-induced physicochemical changes of milk proteins and milk protein stabilized oil-in-water emulsions has been advanced for the last decade. Most of the studies have emphasized on the understanding of how milk-protein-stabilized droplets and the non-adsorbed proteins determine the physicochemical and rheological properties of protein-concentrated dairy colloids. The physical stability of concentrated protein-stabilized emulsions (i.e., against creaming or phase separation/gelation after heat treatment) can be modulated by carefully controlling the colloidal properties of the protein-stabilized droplets and the non-adsorbed proteins in the aqueous phase. This article focusses on the review of the physical stability of concentrated milk protein-stabilized oil-in-water emulsions as influenced by physicochemical factors, interparticle interactions (i.e., protein–protein, and droplet–droplet interactions) and processing conditions. Emphasis has been given to the recent advances in the formation, structure and physical stability of oil-in-water emulsions prepared with all types of milk proteins, reviewing in particular the impact of pre- and post-homogenization heat treatments. In addition, the importance of common components found in the continuous phase of heat-treated nutritional emulsions that can promote aggregation (polymers, sugars, minerals) will be highlighted. Finally, the routes of manipulating the steric stabilization of these emulsions to control heat-induced aggregation—through protein–surfactant, protein–protein, protein–polysaccharide interactions and through the incorporation of protein based colloidal particles—are reviewed.     

One-pot preparation of three-component oil-in-water high internal phase emulsions stabilized by palm-based laureth surfactants and their moisturizing properties

In the present study, olive and olein oils had been used for the preparation of three-component high internal phase emulsions with oil volume fraction of more than 0.77 stabilized by palm-based laureth surfactants for the first time, respectively. These emulsions were easily prepared by one-pot homogenization. The critical micelle concentration and Gibbs energy of the as-synthesized surfactants were determined and discussed. Likewise, the morphology, structural properties, stability and hydration efficacy of the as-prepared emulsions were investigated. Droplet size distribution observed from the optical micrographs was in agreement with the light scattering results which suggested that droplet size increased with increasing ethylene oxide chain length. The rheological measurements of the emulsions at room (25°C) and elevated (40°C) temperatures were interpreted to give clear and direct explanation on the structure and stability of the emulsions. The hydration efficacy of the emulsions was examined in vivo using a corneometer. Both the emulsions containing olive and olein oils, respectively exhibited high stability as indicated by the rheological measurements and the structural properties did not differ from one another. However, olein oil’s hydration efficacy was higher than olive oil’s, suggesting that olein oil could well be a potential moisturizing lipid which might interest the dermatologists.     

FLOW PROPERTIES OF WEATHERED CRUDE OILS AND THEIR EMULSIONS

The present paper proposes the emulsification of weathered crude oils in water as a competitive and cost effective method for reducing their viscosities. Weathered crude oil samples were collected from major Kuwaiti oil lakes. Emulsion preparation involved using, either a nonionic surfactant or alkali, as well as both alkali and fatty acid. The obtained emulsions were characterized by measuring the droplet size distribution of the dispersed phase using optical microscopy. Emulsion stability was also examined in terms of the system breakdown. The rheological properties were measured using a concentric cylinder rotary rheometer. The emulsion rheological behavior has been studied as a function of composition, temperature, and shear rate. A constitutive model was developed to characterize the pseudoplastic behavior of the crude oil and the emulsion systems. The model fitted well the experimental results with a correlation coefficient higher than 95%. Associated with the pseudoplastic behavior, viscoelastic behavior has been observed with emulsions and some oils at high shear rates.

The results of this investigation indicated that the examined weathered crude oils can be transported through pipelines as emulsions of up to 80 vol.% oil concentrations. The proposed method of treatment with NaOH and oleic acid offers several advantages over the surfactant treatment. It exhibited comparable rheological behavior at lower cost and less mixing energy. It also provided higher emulsion stability, which favors oil transportation for longer distances.     

Pickering-stabilized emulsion gels fabricated from wheat protein nanoparticles: Effect of pH,NaCl and oil content

A novel Pickering-stabilized emulsion gel with controlled rheological properties was derived from wheat gliadin nanoparticles-stabilized emulsions by altering preparation conditions (pH, ionic strength or oil content). The formed nanoparticles were relatively small uniform spheres particles (d?相似文献   

Interfacial shear rheology of protein-surfactant layers

The shear rheology of adsorbed or spread layers at air/liquid and liquid/liquid phase boundaries is relevant in a wide range of technical applications such as mass transfer, monolayers, foaming, emulsification, oil recovery, or high speed coating. Interfacial shear rheological properties can provide important information about interactions and molecular structure in the interfacial layer. A variety of measuring techniques have been proposed in the literature to measure interfacial shear rheological properties and have been applied to pure protein or mixed protein adsorption layers at air/water or oil/water interfaces. Such systems play for example an important role as stabilizers in foams and emulsions. The aim of this contribution is to give a literature overview of interfacial shear rheological studies of pure protein and protein/surfactant mixtures at liquid interfaces measured with different techniques. Techniques which utilize the damping of waves, spectroscopic or AFM techniques and all micro-rheological techniques will not discuss here.     

Stability of water/crude oil emulsions based on interfacial dilatational rheology

The dilatational viscoelasticity behaviors of water/oil interfaces formed with a crude oil and its distilled fractions diluted in cyclohexane were investigated by means of an oscillating drop tensiometer. The rheological study of the w/o interfaces at different frequencies has shown that the stable w/o emulsions systematically correspond to interfaces which present the rheological characteristics of a 2D gel near its gelation point. The stability of emulsions was found to increase with both the gel strength and the glass transition temperature of the gel. As expected, the indigenous natural surfactants responsible for the formation of the interfacial critical gel have been identified as the heaviest amphiphilic components present in the crude oil; i.e., asphaltenes and resins. Nevertheless, we have shown that such a gel can also form in the absence of asphaltene in the oil phase.     

Effects of Surface Properties on Rheological and Interfacial Properties of Pickering Emulsions Prepared by Fumed Silica Suspensions Pre-Adsorbed Poly(N-Isopropylacrylamide)

The hydrophobic fumed silica suspensions physically pre-adsorbed poly(N-isopropylacrylamide) (PNIPAM) in water could prepare oil dispersed in water (O/W) Pickering emulsion by mixing of silicone oil. The resulting Pickering emulsions were characterized by the measurements of volume factions of emulsified silicone oil, adsorbed amounts of the silica suspensions, oil droplet size, and some rheological responses, such as stress-strain sweep curve and dynamic viscoelastic moduli as a function of the added amount of PNIPAM. Moreover, their characteristics were compared with those of the O/W Pickering emulsions prepared by the hydrophilic fumed silica suspensions pre-adsorbed PNIPAM. For the emulsions prepared by the hydrophobic silica suspensions, an increase in the added amount of PNIPAM led to (1) a decrease in the volume fraction of the emulsified oil in the emulsified phase, (2) both the size of oil droplets and the adsorbed amount of the corresponding silica suspensions being almost constant, except for the higher added amounts, and (3) both the storage modulus (G′) and the yield shear strain being constant. The term of 1 is the same for the emulsions prepared by the hydrophilic silica suspensions, whereas both the adsorbed amount of the corresponding silica suspension and the G′ value increase and both the droplet size and the yield shear strain decrease with an increase in the added amount of PNIPAM. The differences between the rheological properties of the emulsions prepared by the hydrophilic silica suspensions and those by the hydrophobic ones are attributed to the hydrophobic interactions of the flocculated silica particles in the Pickering emulsions.     

Characterization of Optical Properties in Water-in-Oil Emulsion

There have been few studies on the factors that determine the overall appearance of emulsions. Optical properties are quite important in determining the perceived quality of emulsion-based products. The overall appearance of an emulsion is determined by the way that it interacts with electromagnetic radiation in the visible region of the spectrum, for example, reflection, transmission, adsorption, and scattering. These interactions are principally determined by the characteristics of emulsion droplets (size, concentration, and refractive index). The present study aims at characterizing the optical properties and rheological behaviors of water-in-oil emulsions, especially macroemulsions. There is a decrease in the absorbance spectra as increasing glycerin ratio in aqueous phase because the difference of refractive index between oil phase and aqueous phase decreased, which improved the transparency of water-in-oil emulsion. The absorbance of linear and branched surfactant emulsions were smaller than that of alkyl modified branched surfactant emulsion. Moreover the transparency of emulsions prepared with linear and branched surfactants was much clearer than that of alkyl modified branched surfactant emulsion. The absorbance spectra also showed that low polar oil attributed to the more transparent emulsion, compared with high polar or nonpolar oil. However, these kinds of oils were not helpful to prepare transparent emulsion because the appearance of these emulsions was translucent or opaque, even if polyols in aqueous phase was 30 wt%.     

Rheology and dynamics of micellar cubic phases and related emulsions

The rheological behavior of micellar cubic phases in C12EO25 systems and related emulsions has been investigated. In the aqueous C12EO25 binary system, the transition from the cubic phase to the micellar solution is associated with a sudden drop in viscosity and with a small enthalpy of transition. The elastic modulus and viscosity of the cubic phases show a maximum with concentration but remain very high within the range of existence of the cubic phase. Several relaxation processes seem to be present in binary cubic phases, and some of them occur in a time scale that can be followed by both rheology and dynamic light scattering measurements. Upon addition of a small amount of oil (decane), the rheological behavior changes remarkably. As the oil fraction increases, the relaxation times also increase and, finally, highly concentrated, gel-like emulsions are obtained. Contrary to conventional concentrated emulsions, the viscosity of cubic-phase-based emulsions is decreased by increasing the fraction of the dispersed phase. The non-Maxwellian rheological behavior at low oil fractions is described according to the model of slipping crystalline planes, modified by using a distribution of bulk relaxation times, and good fitting to the experimental data is obtained.     

On the flow characteristics of highly concentrated oil-in-water emulsions

The laminar flow characteristics of oil-in-water emulsions with oil concentrations greater than 59% by volume have been investigated experimentally. Up to an oil concentration of 65% by volume, the emulsions exhibited power-law non-newtonian behaviour. At a higher oil concentration, of 72.21% by volume, a dramatic change in the flow behaviour of the emulsion was observed. The flow curve, i.e. shear stress vs. shear rate plot on a log-log scale, clearly exhibited the presence of a yield-stress.The rheological data on the emulsions were used to correlate the laminar pipeline transport data on the same emulsions. For power-law emulsions, values of the drop in pipeline pressure could be accurately predicted from simple rheological measurements. For a yield-stress emulsion, the experimental pipeline data deviated from the predicted values especially at low values of shear stress.     

Egg yolk protein gels and emulsions

Egg yolk remains a key ingredient of a number of food products. Yet, its main functional properties, e.g. emulsifying ability and gel structure formation, upon heating, have not attracted the attention of too many researchers specializing in the area of food colloids. It is not surprising then that there have been only very few major advances in the field over the period of the last few years. These are discussed in the present review and include recent research findings on competitive adsorption between yolk protein constituents at emulsion oil–water interfaces, and also on the relationship between yolk particle supermolecular structure disorganization and the rheological properties of yolk-based emulsions and gel-network structures.